Integrated circuits are commonly used to provide critical safety operations due in part to their high level of reliability and their ability to economically combine many functional blocks onto a single chip. One such integrated circuit is the prevention electronics circuit embedded in rechargeable lithium-ion battery packs used to detect and limit improper charging conditions.
When a functional block fails on an integrated circuit, catastrophic results may occur. For example, if a functional block that determines the temperature on the prevention electronics embedded in a battery pack fails, the battery's life could be diminished, or worse, the battery could explode. Some integrated circuits include redundant functional blocks to help ensure proper operation of the circuit in cases where one of the functional blocks fails. In the above example, for instance, if a redundant functional block to determine the temperature on the chip is included, the potential problems may be avoided.
Functional blocks on a chip may be connected in such a way that nonfunctional blocks are bypassed or at least cause fail-safe operation. As a result, a failure in any one functional block may not impede the overall operation of the circuit. Therefore, it may not be possible that a failure on a chip be discernable from an external measurement or inspection.